- the analogue signal is partially diverted with the aid of a diverter,
- the partially diverted analogue signal is rectified by a rectifier so as to obtain a pulse comb,
- the pulse comb is thereafter conveyed to a resonator, tuned to a frequency which is a multiple of that of the digital samples,
- if and only if the analogue signal has been synthesized on the basis of the said digital samples, the resonator enters resonance and is sustained,
- finally, a detector detects the energy level accumulated by the resonator and compares it with a detection threshold making it possible to generate a validity signal.

Advantageously, in the method for detecting the digital origin of an analogue signal according to the invention, the analogue signal being emitted by a digital-analogue converter on the basis of digital samples, and exhibiting a discretization level related to the said digital-analogue converter, the resonator/detector assembly is designed in such a way that, once the detection threshold has been reached, making it possible to guarantee the digital origin of the analogue signal, the resonator can be sustained by a succession of digital samples differing between them of the lowest available discretization level at the output of the said digital-analogue converter.

The invention also resides in a device for detecting the digital origin of an analogue signal, intended for an onboard alarm management system, and making it possible to implement the previously described method according to the invention, an analogue signal being conveyed to the input of the said device, the said device comprising:

- a diverter,
- a rectifier,
- a resonator,
- a detector,
- making it possible to provide a validity signal determining the digital or non-digital origin of the said analogue signal.

Advantageously, the said validity signal is binary.

Advantageously, an alarm management system carried onboard an aircraft, comprising a device for generating announcements of faults or information intended for the pilot, in the form of analogue synthesis signals, can comprise a device for detecting the digital origin of an analogue signal according to the invention.

Advantageously, the device for generating announcements of faults or information intended for the pilot comprises a list of digital samples of which a series of digital samples is emitted towards a digital-analogue converter at the output of which the analogue signal is conveyed to the said device for detecting the digital origin of an analogue signal which diverts a fraction thereof, the remainder of the said analogue signal passing through a low-pass filter providing a final analogue signal which, if the validity signal guarantees the digital origin of the analogue signal, ends up at a loudspeaker device.

Advantageously, a security bit attesting to the integrity of the analogue signal synthesized on the basis of the emitted series of digital samples is generated and associated with the validity signal.

Advantageously, the list of digital samples can comprise inaudible sounds, the digital origin and validity of which are detected by the device for detecting the digital origin of an analogue signal.

Advantageously, the resonator is tuned to a frequency which is a multiple of that of the digital samples.

Advantageously, an alarm management system can comprise at least one second device for generating announcements of faults or information intended for the pilot.

Advantageously, the device for detecting the digital origin of an analogue signal makes it possible to select the priority device for generating announcements of faults or information intended for the pilot.

Advantageously, when a sole device for generating announcements of faults or information intended for the pilot detects a fault, the said alarm management system informs the pilot thereof, enabling him to conclude that there is a possible malfunction of the said sole device for generating announcements of faults or information intended for the pilot that detected a fault.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become apparent with the aid of the description which follows in conjunction with the appended drawings which represent:

FIG. 1: the diagram of the principle of the invention;

FIG. 2: the diagram of a simple exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 represents the principle of the device for detecting the digital origin of an analogue signal according to the invention. This device is situated within an alarm management system capable of generating “voice announcements” based on a set of digital samples NUM. In the case of faults or when information must be provided, to the pilot of an aircraft for example, a series of digital samples can be emitted. This series of digital samples is converted into an analogue signal by a digital-analogue converter DAC. It is at the output of the said digital-analogue converter DAC that the device for detecting the digital origin of an analogue signal is preferably placed. In all cases, it must be supplied with theanalogue signal1 before the latter is smoothed, as here by the low-pass filter PB. Indeed, at the output of the digital-analogue converter, theanalogue signal1 exhibits a “staircase” appearance, which will be detected so as to determine the digital origin of the signal. The diverter DER of the device diverts afraction2 of theanalogue signal1. Thisfraction2 of theanalogue signal1 is thereafter rectified by the rectifier RED so as to obtain apulse comb3. Thispulse comb3 then excites a resonator RES tuned to a frequency which is a multiple of that of the digital samples. Therefore, if theanalogue signal1 does indeed arise from a combination of digital samples of the set NUM, the resonator RES enters resonance and is sustained, providing as output a signal4 comprising resonance spikes. At the extremity of the chain the detector DEC compares the signal4 arising from the resonator RES with adetection threshold5. If the resonator RES is in resonance, thedetection threshold5 is reached. Consequently, the detector DEC provides a binary signal corresponding to the validity signal VAL. The validity signal VAL can thereafter be utilized by the system so as to decide to let the voice announcement MSG reach the loudspeaker HP.

The idea is therefore to detect the “staircase” appearance of theanalogue signal1. The device according to the invention makes it possible to guarantee the digital origin of the saidanalogue signal1, before the latter is filtered and conveyed to the loudspeaker HP. In the case of an onboard alarm management system comprising several sub-assemblies for detecting and generating announcements of faults or information, this helps with the secure selection of the priority sub-assembly. Indeed, the fault modes of equipment such as the digital-analogue converter DAC or amplifiers possibly present in the voice announcement-generating chain, and which may generate noise, do not run the risk of being recognized as genuine messages and they cannot reach the loudspeaker HP nor give rise to the retaining of the priority status by the device which comprises them.

It should be noted that it is advantageously possible to combine the validity signal VAL emitted by the device according to the invention with a security bit guaranteeing the integrity of the series of digital samples ending with the generation of theanalogue signal1 and then with the voice announcement MSG. The definition and the utilization of such a security bit are described in French patent No. FR2723222A1. The association of the security bit and of the validity signal VAL makes it possible to reach a very high security level.

FIG. 2 illustrates an exemplary embodiment of the device according to the invention, based on a very simple electronic circuit. The diverter DER consists of a simple capacitor C1 making it possible to divert a low-energy fraction2 of theanalogue signal1. The rectifier RED is, basically, composed of two diodes D1 and D2 making it possible to convey a pulse comb to the resonator RES. The resonator RES comprises a capacitor C2 and an inductor L in parallel. The values of the capacitor C2 and of the inductor L are such that the resonant frequency of the said resonator RES, in this instance

(\frac{1}{2 \cdot π \cdot \sqrt{L \cdot C 2}}),

is a multiple of the frequency of the constituent digital samples of the set of digital samples NUM. If theanalogue signal1 is based on the said digital samples, the resonator RES enters resonance. To finish, the detector DEC comprises a diode D3 followed by a resistor R1 of high impedance and a capacitor C2 in parallel with a second resistor R2. The comparator COMP is charged with comparing the signal arising from this circuit with a detection threshold. If this threshold is reached, the validity signal VAL is true. It is false in the converse case. The true or false state of the validity signal VAL conditions the access of the voice announcement MSG to the loudspeaker HP.

Furthermore, with the device according to the invention, moments of silence can without any problem be integrated into the voice announcements without any risk of being interpreted as invalid. Indeed, these silences must simply be coded as inaudible sounds, consisting of an alternation of samples of zero mean value, but enabling the resonator RES to be sustained. Likewise, the device according to the invention applies without any restriction to an analogue signal which might arise from a mixture of several voice synthesis sources.

To summarize, the device according to the invention exhibits the essential advantage of making it possible to guarantee the digital origin and the integrity of an analogue signal; it is intended for alarm management systems carried onboard aircraft and fitted with devices for generating voice announcements.